The present invention relates to syringes, particularly to syringes of the type including a barrel having an apertured end wall, a plunger assembly movably received within the barrel and including an outer shaft and an inner piston, and finger-gripping elements on the barrel and plunger shaft enabling the latter, and thereby the piston, to be manually moved towards the apertured end wall of the barrel for injecting fluid therethrough.
Devices of the foregoing type are commonly used as hypodermic syringes for injecting fluid into body cavities. Normally it is important, and sometimes quite critical, to inject the fluid at a predetermined pressure, which is usually determined by "feel". However, "feel" is far from satisfactory in many cases as it depends on the experience and skill of the user, and also on the peculiar parameters (e.g., size and sliding-friction of the piston) of the specific syringe being used. Some syringes are equipped with manometers for indicating the pressure of the fluid as it is being injected. However, manometers add substantially to the expense of the syringe; moreover, they are very awkward to use, and frequently the operator does not bother to use one even when available.